class Solution(object):
    def calPoints(self,ops):

result=[]
for i in ops:
s=len(result)
if i=="+":
result.append(result[s-1]+result[s-2])
elif i=="C":
result.pop()
elif i=="D":
result.append(result[s-1]*2)
else:
result.append(int(i))
return sum(result)
a=Solution()
print(a.calPoints(["5","2","C","D","+"]))